1. Field of the Invention
The present invention relates to a novel radiation curable release agent and, more particularly, a radiation curable silicone release agent that has low viscosity even without a solvent, excellent thin film coating performance and, furthermore, an excellent cure rate and excellent release properties. Moreover, the present invention relates to a separator using this release agent.
2. Description of the Related Art
It is well known that forming a coating by curing, on the surface of a substrate such as paper of various types, synthetic film, or a textile, a composition containing as a main component a polyorganosiloxane, imparts release properties to the coating with respect to tacky materials.
With regard to such silicone release agents, those that are cured by a condensation reaction (ref. JP-A-47-34447 (JP-A denotes a Japanese unexamined patent application publication), etc.), and those that are cured by an addition reaction (ref. JP-B-52-40918 (JP-B denotes a Japanese examined patent application publication), etc.) are known. In order to carry out these curing reactions it is necessary to apply heat, and there is therefore the drawback that the application thereof is limited to substrates that can withstand the curing temperature.
In order to eliminate this drawback of thermosetting type silicone release agents, various types of ultraviolet curable silicone compositions have been developed (ref. JP-A-1-297421 and JP-A-1-311103). These methods have the advantages that the curing time is usually short, and substrates that are susceptible to damage by thermal energy can be employed since curing is carried out, without heating, by ultraviolet irradiation after coating.
With regard to conventional ultraviolet curable silicones, a variety of curing modes have been proposed. Among them, a type in which a polyorganosiloxane having an epoxy group or a vinyl ether group in the molecule is cured by a reaction involving ultraviolet radiation in the presence of a cation-generating type catalyst is excellent since the curing thereof is not inhibited by oxygen and there is no unpleasant odor, and the use thereof is being widely investigated.
In general, in the case where a polyorganosiloxane composition that is cured by ultraviolet radiation is used as the release agent, in order to meet various requirements for the properties of the release agent such as coating performance, coating formation properties, and release properties, it is necessary to take into consideration the molecular structure, the molecular weight, etc. of a photoreactive polymer. With regard to conventional ultraviolet curable release agents having an oxirane functional group such as glycidoxy or 3,4-epoxycyclohexyl that have been proposed as photo-cationic curing type release agents, it is difficult to obtain a cured coating exhibiting a low release force. In particular, in the case of a glycidoxy group, since the curing speed is slow, recent demand for a high curing speed in order to increase the productivity cannot be fulfilled satisfactorily. In the case of a vinyl ether functional group, synthesis of a photoreactive polymer is complicated, and is undesirable in terms of cost. With respect to the reactive groups, it has also been suggested as disclosed in, for example, JP-A-12-265153 that the release properties and the curing properties can be adjusted and improved by introducing an oxetanyl group into a silicone molecule.
In general, when coating the release agent it is necessary to make the coated film very thin. Although conventional release agents have comparatively low viscosities, since it is difficult to form a coating having a thickness of 1 μm or less without using a solvent, they are often diluted with an organic solvent for coating, thus causing environmental issues due to discharge of the organic solvent.